Screw-Advance Box Joint Jig

This jig is based on the box joint jig designed by Matthias Wandel at www.woodgears.ca . If you haven’t seen his site, you should check it out – a ton of great ideas for shop machinery you can build yourself.

I made a few modifications to the original design to fit my work style:

I moved the crank mechanism to the right and oriented the primary gear vertically, which I thought would make it more comfortable for me to use.

I use fractional inches in most of my work, so I designed the system with that in mind. The screw pitch is 16 TPI, so one turn advances the jig 1/16”. The primary gear is four times the size of the drive gear, so a full turn on the crank gives me 1/4” advance. I designed the primary gear assembly so it could be changed to different size gears, but so far I’ve only used the one size.

I didn’t trust myself to always turn the crank exactly a full turn (and I’m the sort of guy who can lose count between one and three), so I added a scale to the fixed fence and an indicator on the carriage. For additional accuracy, I added an indicator by the drive gear and colored the indicator and “zero” tooth red. This also gives me the flexibility to make joints in increments that are a multiples of 1/8” and even multiples of 1/16” without building additional primary gears, but would require making partial turns on the primary gear. However, the smallest joints I have made are 1/8”, which requires 1/4” advance – one full turn of the crank.

The carriage rides on two sliding dovetails. I’m a little fixated on sliding dovetails, and even make full-extension drawer slides out of them sometimes. The carriage is tight enough between the dovetails that there is no noticable movement.

In an effort to save a couple of dollars, I used a seamless sleeve instead of a bearing for the screw. That was a mistake, as the side load on the gear creates quite a bit of friction. I’ll replace it with a bearing soon.

The last two pictures are the largest and smallest boxes I’ve made with the jig so far. The big box is a book-return drawer for our local library with ½” x ¾” box joints. Yes, I cleaned up the glue before installing it! The little box is for my dial calipers and has 1/8” x ¼” joints.

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23 comments so far

Nice work. I have considered building this myself. Did you find the plans easy to follow?Did you cut 4 ends at a time when making the fingers?I will second peter in saying that www.woodgears.ca is an awesome site and he posts a new article every monday.

Thanks for the comments! I actually didn’t buy the plans (sorry Matthias), but just read the blog and designed from there. However, given the clarity and depth of information on the website, I bet the plans will be great.

@BeeMan – yep, I cut all four boards at once, so you only have two setups to cut all the joints for a box. It’s pretty slick.

If you’ve been thinking about building it – get to it, you’ll love it! I almost never use my dovetail jig anymore.

Ho, Peter!!! I see you’re still at it in a grand way. Great jig and probably as useful as all get out. I’m thinkin’ of ya while enjoying the warm here in south California. Only got to 83 today. DANG!!!

I’m getting ready to build a batch of 20 drawers, so this thing is going to get a workout again really soon. It’s really not too hard to build, and the increased productivity is definately worth the effort.

@Thos – great to hear from you! Maybe I’m crazy, but I like my Idaho weather. There is just something wrong about 83 degrees in December. Of course, I might feel differently after a few winters in Jordan Valley!

@Attainable – That’s a good question. I didn’t really calculate the cost. All of the lumber was on-hand. If you had to buy a full-sheet of good ply to make the base, that would really drive up the cost compared to the cost of the few sqft I actually took from stock. I would estimate materials at about $30-40 on this. If you purchase the plans from woodgears.ca that would put your cost closer to $50.